Some conveyors use a moving belt to convey items from one point to another. The conveyors have pulleys or rollers on each end that keeps the tension on the belt at a predetermined tension. A motor coupled to the belt or a motorized pulley may move the belt. When the belt is under tension, there is friction between the motorized pulley and the belt that enables the pulley to grab the belt and move the belt as the pulley rotates.
The motorized pulleys are very difficult to implement when the conveyor is curved. More specifically, the belt on a curved conveyor tends to migrate toward the center of the radius of the curve, which causes the pulleys to lose contact with the belt. Accordingly, the belt loses tension so there is no friction between the belt and the pulley and movement of the belt stops.
A chain or other device attached to the belt may be used to move the belt around a curve. A sprocket may move the chain in a conventional manner, which in turn causes the belt to move. The sprocket has several components associated with it and tends to limit the amount of force that the belt uses to move an item.